Some further information is desired as to the armament for which these mantlets are intended. They were originally adopted for embrasures cut down into a parapet to suit guns mounted on ship truck carriages, which left a large opening to be covered over the gun. Now, in our siege batteries from the top of the 32-pounder, when in battery, to the crest of the parapet is only one foot nine inches to be covered by the mantlet, and with the siege 4½-inch ordnance gun, one foot four inches. This small space over the gun closed by rope gives but very little strength, in addition to which the rope is not musket or rifle proof at 200 yards. These considerations induced me to send you at Yorktown in 1862 wood and boiler-iron mantlets, with a box of chisels to cut the iron to suit your guns. A part of these old ones have lately been found by Stewart at Suffolk and sent forward; that may suffice for some fifty or sixty guns, giving me time to learn your wishes in regard to others to be forwarded and to learn the size of the guns. If made of rope you cannot alter them to suit guns of different exterior diameters, but it made of wood and iron you can enlarge the opening at pleasure. The splinters from the wood and iron are objectionable produced by artillery. During such a fire they would probably be withdrawn and used to guard against infantry fire only. While the rope would not give splinters, yet at the same time would not be proof against the rifle musket-balls. Advise me from Old Point by telegram; say “rope” or “iron and wood” and I will understand you. Also give diameters of guns, exterior.

To answer this question, Barnard turned to Hunt. And Hunt consulted Abbot.

First off, you might ask what are mantlets? Well let us start with what an embrasure is – “an opening made in the parapet for a gun to fire through.”

The definition and illustration come from John Tidball’s 1891 Manual of Heavy Artillery. Looking at Figure 4 – the right side and upper center – we see the cut through the parapet allowing the muzzle of the cannon an unobstructed line to fire out. And we see Tidball offered views of direct, oblique, and high angle embrasures. But, there are two tactical problems here. First is maintenance. The force and shock of firing would in time erode and enlarge the opening. Since the embrasure faced the enemy, simply spading more dirt into place was not practical. So common practice was to place raw-hide, gabions, or other reinforcement around the embrasure. Tidball preferred iron plates to form a lining of the embrasure, as depicted in Figure 5 (to the left).

But that leaves us with the other problem – if the gun could fire out, the enemy could fire in! In Figure 5, Tidball demonstrated the use of an iron plate as a mantlet, which he defined as “a shield placed over the mouth of an embrasure to prevent musketry bullets and fragments of shells from flying through and injuring those serving the piece.” (And recall the batteries on Morris Island used similar iron linings and mantlets, formed from the boilers of the blockade runner Ruby in 1863.) A door in the center, roughly a foot high and six inches wide, allowed the crew to pass a rammer through when loading, sight down the piece, and project the muzzle. The preference was to make that opening as small as practical, still allowing for the service of the piece.

As alluded by Delafield, iron was not the only material that could serve as a mantlet. Wood and iron, though resistant to blast damage and musket fire, had the disadvantage of producing splinters. Rope, as Delafield stated, didn’t have the splinter problem, but was not considered stiff enough to resist musketry. But what Delafield apparently didn’t take into account were experiments by Abbot to devise a better rope mantlet, as he advised Barnard about responding to Delafield:

I decidedly prefer the rope mantlets. I find by trial at twenty paces that the penetration of our Springfield rifle, elongated bullet, is between two and two and five-tenths inches. The mantlets are six inches thick and they are thus perfectly rifle-proof. Their dimensions are the following, which are very convenient in practice:

The opening can readily be cut larger if necessary. We have done so at least in one instance, to enlarge the traverse of the gun in an oblique embrasure. The men are afraid of splinters from a cannon-ball-and I think justly so–with the wood and iron mantlets. Moreover, the blast of a light 12-pounder has already rendered unserviceable one of the iron mantlets of this pattern.

I therefore entirely agree with yourself and General Hunt in thinking that only rope should be ordered. I think the dimensions cannot be improved. As to number required, my train proper, which is entirely distinct from my present guns, consists of forty-six guns requiring mantlets, and ten 8-inch siege howitzers which I think can hardly be used with them. I have here seventeen rope mantlets and twenty-three wood and iron, one of the latter unserviceable. As they are very liable to be destroyed, and moreover are quite useful even for light guns when sharpshooters are as troublesome as they have been here at times (I have had two men killed besides some wounded in my own regiment by them already), I think that about 100 could be safely ordered (besides those I have on hand). They should be made of tarred rope, like the old ones.

So with a thicker set of ropes, the gunners were better protected.

Turning back to Tidball’s post-war manual, he offered two illustrations of rope mantlets:

Figure 2 above matches somewhat to the second illustration offered by Abbot in 1864. The use of rope afforded some flexibility for those working at the muzzle with rammers and sponges. Tidball stated those mantlets weighed 400 pounds. Figure 3 appears to be a more refined fitting, which I would question in regard to ease servicing the weapon.

Without mantlets, sharpshooters could reduce the efficiency of the guns, if not silence them completely. Thus these relatively minor devices became rather important as the army transitioned into siege operations. In fact, I dare say any work discussing the fortifications at Petersburg, at a tactical level, should include a proper discussion of mantlets… lest the author be accused of dealing with the subject lightly.

(Citations from OR, Series I, Volume 40, Part II, Serial 81, pages 21, 223-4; John C. Tidball, Manual of Heavy Artillery Service: For the Use of the Army and Militia of the United States, Washington, D.C.: James J. Chapman, 1891, pages 385-6, 399, and Plates 61 and 68.)